1. Field of the Disclosure
Embodiments of the present disclosure relate to a push-button switch, and particularly to a push-button switch for engine start which is used in an immobilizer system in a vehicle.
2. Description of the Related Art
In moving vehicles, such as automobiles, of the related art, an engine is started by inserting a key into a key hole and operating the key. Recently, a so-called immobilizer system in which an engine is started without inserting a key into a key hole has been used for convenience. The immobilizer system has a configuration having high security in such a manner that an authentication function for engine start is provided and that, when the authentication is not established between the main body of an automobile and a portable device, the engine does not start. When the authentication is established between the main body of an automobile and a portable device, the engine starts by pressing a push-button switch attached to the vehicle.
Thus, the immobilizer system has a configuration in which an authentication operation is performed through communication between the main body of an automobile and a portable device. If the remaining battery level of the portable device becomes equal to or lower than a predetermined value, communication between the main body of an automobile and the portable device may fail to be performed. To avoid this situation, a push-button switch for engine start includes a transmission/reception antenna as communication means for emergency. The portable device is held close to the switch for engine start, whereby power may be supplied from the transmission/reception antenna to the portable device in a non-contact manner, and the communication may be also performed.
A transmission/reception antenna similar to the transmission/reception antenna used in the above-described push-button switch for engine start is disclosed in U.S. Patent Application Publication No. 2012/0119965. FIG. 11 illustrates the configuration of a transmission/reception antenna 904 described in U.S. Patent Application Publication No. 2012/0119965.
The transmission/reception antenna 904 of FIG. 11 includes a magnetic member 911, a excitation loop antenna 912 disposed on the magnetic member 911, a transmission/reception loop antenna 913 which is disposed close to but not in contact with the excitation loop antenna 912, and a resonance capacitor 914 connected to both ends of the transmission/reception loop antenna 913. The excitation loop antenna 912 includes a loop portion 912a with a single turn. The transmission/reception loop antenna includes a loop portion 913a with more than one turn. The excitation loop antenna 912 and the transmission/reception loop antenna 913 are attached to the top surface of a base board 921 in such a manner that the excitation loop antenna 912 and the transmission/reception loop antenna 913 are coaxially wound around a columnar portion of the magnetic member 911.
By holding a wireless communication medium, such as an integrated circuit (IC) tag or a non-contact IC card, on the upper portion side of the magnetic member 911, that is, the opposite side of the base board 921, the transmission/reception antenna 904 having this configuration is capable of supplying power to the wireless communication medium and receiving/transmitting a signal from/to the wireless communication medium, achieving broadband frequency characteristics without increasing the power consumption.
However, when the coil antenna having a loop portion wound around the magnetic member, as described in U.S. Patent Application Publication No. 2012/0119965, is applied to a transmission/reception antenna in a push-button switch for engine start which is used in an immobilizer system in a vehicle, there arises the following problem.
In the case of a push-button switch for an immobilizer system, a switching mechanism having switching contacts and driving members is disposed on the top surface of the wiring board to which the portable device which is a wireless communication medium comes close. In addition, such a coil antenna needs a relatively wide area for attachment. As a result, on the top surface of the wiring board, there remains only an extremely small area for attaching the coil antenna having a coil conductor wound around the magnetic core. Therefore, the coil antenna has to be attached to the bottom surface of the wiring board. However, when the coil antenna is attached on the bottom surface of the wiring board, the distance from the portable device is long, and communication with the portable device may fail to be performed.
These and other drawbacks exist.